1. Field of the Invention
The invention relates to the technology of making optical DWDM (Dense-Wavelength-Division-Multiplexing) multiplexor or demultiplexor, and particularly to the DWDM multiplexor or demultiplexor provided with a pair of so-called built-in V-groove dual fiber collimators.
2. The Related Arts
The future communication networks demands ever increasing bandwidth. By transmitting several channels in a single optical fiber at different wavelengths. DWDM can dramatically enhance the transmission capacity of the optical fiber communication systems. A devices that combines different wavelength channels into one fiber is a multiplexor, and a device that divides the multiplexed channels into individual ones is a demultiplexor. A variety of technologies have been exploited to develop high performance DWDM multiplexor/demultiplexor, including fiber Bragg grating, optical integrated circuit, fused fiber Mach-Zander interferometer, interference thin film coating technology etc. An international standard wavelength grid has been suggested by the ITU (International Telecommunication Union) for the center wavelengths of the DWDM channels. Generally, the center wavelength of a band-pass optical filter is tuned to the ITU grid by the incident angle of the beam onto DWDM bandpass filter. The prior art uses an Y-branch structure of three conventional fiber optic collimators. The incident angle is tuned by changing the angles between the associated collimators, and thus the center wavelength of such a multiplexor/demultiplexor is made to coincide with a desired ITU wavelength. The disadvantage in the prior art is mainly in difficulties to reduce the size of the assembly for achieving a robust and compact structure. The relates references include U.S. Pat. Nos. 4,464,022, 5,204,771, 5,574,596, 5,629,955, 5,712,717, 5,748,350, 5,764,825, 5,786,915, 5,799,121 and 5,808,763.
Therefore, it is desired to provide a DWDM multiplexor/demultiplexor with characteristics of the compact and robust structure, lower cost and flexibility in manufacturing, and high stability in hazardous environment.
According to an aspect of the invention, a multi-port fiber optic device includes a pair of opposite collimators, of which at least one includes a V-groove dual fiber ferrule, and each has a GRIN rod lens. At least one band-pass DWDM thin film filter is securely sandwiched between the two opposite GRIN rod lens of the pair of collimators. The V-groove dual fiber ferrule is used to couple light in and out thereof and tune the thin film filter center wavelength to the ITU grid. The light coupled in from the input fiber of the V-groove dual fiber ferrule will be collimated and transmitted to the DWDM thin film filter. The part of the in-pass-band light will pass through the filter as performing a demultiplexed channel and is successively coupled into the other collimator aside. On the other hand, the out-pass-band is coupled back into the output fiber of the V-groove dual fiber ferrule for being transmitted to the next stage for demultiplexing other channels. The epoxy joints are applied among the filter, the GRIN rod lens and the V-groove ferrule. The two opposite collimator are aligned with each other for the minimum loss therebewteen and the minimum size of the total assembly.